Heat transfer modes

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Cooling plate

A flat aluminium channel assembly under or between the cells through which coolant, usually a water–glycol mix, is pumped. Heat crosses from cell to plate through a thermal interface material; the plate also sets the pack’s temperature uniformity.

Heat transfer coefficient

The heat carried away per unit area per kelvin of difference between a surface and the fluid passing it. Typical values are 5–25 W/(m²·K) for still air, 25–250 for forced air and hundreds to thousands for pumped liquid, which is why fast-charging packs are liquid-cooled. Thermal models use it as their cooling boundary.

Thermal conductivity

How readily a material conducts heat: the heat flux per unit temperature gradient. Cells are strongly anisotropic — around 25–45 W/(m·K) in-plane, along the metal foils, but below 1 W/(m·K) through-plane, across separators and coatings — so the side a cell is cooled from decides how hot its core runs.

Thermal propagation

Thermal runaway spreading from one cell to its neighbours through conducted heat, hot gas and flame. Pack designs are judged by whether, and how slowly, a single failing cell takes the rest with it.

Thermography

Imaging surface temperature with an infrared camera, which converts the radiation a surface emits into a temperature map. It reveals hot welds, busbar joints and uneven cell heating at a glance, but bare metal reflects more than it emits, so shiny surfaces are usually coated matt black before measuring.

References & further reading

Technical references

1. University Physics Volume 2, §1.6: Mechanisms of Heat Transfer

   OpenStax, Rice University

   Technical reference · Conduction, convection, radiation and thermal resistance.

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

2. A General Energy Balance for Battery Systems

   Dawn Bernardi, Ellen Pawlikowski, John Newman · Journal of The Electrochemical Society · 1985

   Topic background · Battery energy balance and irreversible and reversible heat contributions. Reduced thermal models require explicit assumptions and current-sign conventions.